Nylon can be dyed with acid dyes and therefore it can also be stained by natural or artificial acid dyes existing in some foods and drinks when they are spilled on nylon fabrics or carpets. The current way of avoiding such staining is to topically apply to the surface of the filaments materials which function as stain-blockers or stain-resist agents, thus preventing acid stains from permanently coloring the yarn. Such treatment, however, can be costly.
Alternatively, it is known from Flamand U.S. Pat. No. 3,542,743, Crampsey U.S. Pat. No. 3,640,942 and Ucci U.S. Pat. No. 4,579,762 that small amounts of certain materials which confer cationic dyeability on nylon, such as aromatic sulfonates and their alkali metal salts, may be copolymerized with the nylon as a means of rendering the nylon resistant to staining by acid dyes.
Recently, yarn producers have begun incorporating colored pigments into nylon yarns to improve their resistance to degrading and fading in ultraviolet light, to give improved resistance to chemicals and noxious fumes and to give permanent coloration which is not removed by washing. However, when light shades of pigment are used, acid dye stains from accidental spills are visible on the surface of the filaments.
While some pigments can be mixed easily into the nylon without adversely affecting the filament spinning operation, most pigments cause some difficulties while being mixed into the nylon or in subsequent spinning and drawing operations. In general, organic pigments cross link nylon, raise its viscosity, form spherulites which weaken the fibers and cause increased draw tension and filament breaks. Many inorganic pigments depolymerize the nylon, raise the number of amine ends (thereby increasing the susceptibility of the nylon to acid dye stains), lower the viscosity and also form spherulites. For example, pigments containing iron oxide or zinc ferrite and particularly a combination of the two give very poor operability. Either type of pigment in large particles weakens the fibers, clogs the spinning pack filters and causes breaks. On the other hand, very finely divided pigment agglomerates to form larger masses of varying size, causing the same problems as large particles, but such masses also color the polymer unevenly and less effectively due to poor dispersion of the pigment in the polymer.
The depolymerization caused by inorganic pigments is usually worse in the processing of nylon 6,6 than in nylon 6 because of the higher melting temperature of nylon 6,6 and the more reactive nature of nylon 6,6.
Ultraviolet light degrades nylon, and the degradation is accelerated by the presence of certain pigments, particularly metal oxides such as titanium dioxide. To avoid this, copper in various forms is often added to the polymer, but a portion of the copper deposits on internal surfaces of equipment which contacts the polymer. Such difficulty is disclosed in Elbert et al. U.S. Pat. No. 3,565,910. In addition, an amount of copper which is effective in preventing degradation of the polymer by ultraviolet light also causes poor spinning performance. The combination of pigment and copper is still worse.
Ways of avoiding the need to topically stain-proof pigmented nylon filaments and overcoming processing problems caused by the pigment and copper would be greatly desired. It would be particularly useful to be able to use a wide selection of colored pigments, both organic and inorganic, in order to make a complete range of styling colors without encountering serious product deficiencies or operating difficulties with any of them.